Uses of Dynamic allocation on vector(iox::cxx::vector) ?

[givesun]

I'm interested in iceoryx_hoofs and I have few questions.

I understood the goals of iceoryx_hoofs is to remove dynamic allocation and use fixed static memory.

When I saw the iox::cxx::vector and api emplace_back, There are few point to use dynamic allocation like the followings.

{code}
template <typename T, uint64_t Capacity>
template <typename... Targs>
inline bool vector<T, Capacity>::emplace_back(Targs&&... args) noexcept
{
if (m_size < Capacity)
{
new (&at(m_size++)) T(std::forward(args)...);
return true;
}
return false;
}
{code}

There is a code to use 'new', I think this is the code using heap.
Is this the right? Or Could you please teach me If I mis-understand?

[elfenpiff]

@givesun Here you are mistaken. new has in the end to options:

• allocate memory on the heap and create an object at the heap memory location.
• create an object at the provided memory location

The difference is subtle but in this case we provide the memory location in the first bracket (&at(m_size++)) and then call the constructor of T with T(std::forward(args)...) which results in

new (&at(m_size++)) T(std::forward(args)...);

If we would allocate this on the heap the call would look like:

new T(std::forward(args)...);

If you would like to dive deeper into placement new take a look at this article: https://en.cppreference.com/w/cpp/language/new#Placement_new

[givesun]

@elfenpiff
Thanks for your kindly explanation.
I've knew another usage of 'new' operation.
Thanks.